R help - Jan 2005 - Finding "runs" of TRUE in binary vector

I have a binary vector and I want to find all "regions" of that vector
that are runs of TRUE (or FALSE).

 > a <- rnorm(10)
 > b <- a<0.5
 > b
  [1]  TRUE  TRUE  TRUE FALSE  TRUE FALSE  TRUE  TRUE  TRUE  TRUE

My function would return something like a list:
region[[1]] 1,3
region[[2]] 5,5
region[[3]] 7,10

Any ideas besides looping and setting start and ends directly?

Thanks,
Sean

Untested:

c(TRUE, b[-1] != b[-length(b)]) gives you the (logical) indexes of the
beginnings of the runs
c(b[-1] != b[-length(b)], TRUE) gives you the (logical) indexes of the
ends of the runs
> -----Original Message-----
> From: r-help-bounces at stat.math.ethz.ch 
> [mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of Sean Davis
> Sent: Thursday, January 27, 2005 2:14 PM
> To: r-help
> Subject: [R] Finding "runs" of TRUE in binary vector
> 
> I have a binary vector and I want to find all "regions" of 
> that vector that are runs of TRUE (or FALSE).
> 
>  > a <- rnorm(10)
>  > b <- a<0.5
>  > b
>   [1]  TRUE  TRUE  TRUE FALSE  TRUE FALSE  TRUE  TRUE  TRUE  TRUE
> 
> My function would return something like a list:
> region[[1]] 1,3
> region[[2]] 5,5
> region[[3]] 7,10
> 
> Any ideas besides looping and setting start and ends directly?
> 
> Thanks,
> Sean
> 
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide! 
> http://www.R-project.org/posting-guide.html
>

Thanks Patrick, Albyn, and Vadim.

rle() does what I want and, Vadim, your method gives the same results 
in a different form.  I appreciate the help!

Sean

On Jan 27, 2005, at 5:29 PM, Vadim Ogranovich wrote:
> Untested:
>
> c(TRUE, b[-1] != b[-length(b)]) gives you the (logical) indexes of the
> beginnings of the runs
> c(b[-1] != b[-length(b)], TRUE) gives you the (logical) indexes of the
> ends of the runs
>
>> -----Original Message-----
>> From: r-help-bounces at stat.math.ethz.ch
>> [mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of Sean Davis
>> Sent: Thursday, January 27, 2005 2:14 PM
>> To: r-help
>> Subject: [R] Finding "runs" of TRUE in binary vector
>>
>> I have a binary vector and I want to find all "regions" of
>> that vector that are runs of TRUE (or FALSE).
>>
>>> a <- rnorm(10)
>>> b <- a<0.5
>>> b
>>   [1]  TRUE  TRUE  TRUE FALSE  TRUE FALSE  TRUE  TRUE  TRUE  TRUE
>>
>> My function would return something like a list:
>> region[[1]] 1,3
>> region[[2]] 5,5
>> region[[3]] 7,10
>>
>> Any ideas besides looping and setting start and ends directly?
>>
>> Thanks,
>> Sean
>>
>> ______________________________________________
>> R-help at stat.math.ethz.ch mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide!
>> http://www.R-project.org/posting-guide.html
>>

Sean Davis <sdavis2 at mail.nih.gov> writes:
> I have a binary vector and I want to find all "regions" of that
vector
> that are runs of TRUE (or FALSE).
> 
>  > a <- rnorm(10)
>  > b <- a<0.5
>  > b
>   [1]  TRUE  TRUE  TRUE FALSE  TRUE FALSE  TRUE  TRUE  TRUE  TRUE
> 
> My function would return something like a list:
> region[[1]] 1,3
> region[[2]] 5,5
> region[[3]] 7,10
> 
> Any ideas besides looping and setting start and ends directly?
You could base it on
> rle(b)
Run Length Encoding
  lengths: int [1:5] 1 1 2 4 2
  values : logi [1:5]  TRUE FALSE  TRUE FALSE  TRUE
> b
 [1]  TRUE FALSE  TRUE  TRUE FALSE FALSE FALSE FALSE  TRUE  TRUE

(Notice that my b differs from yours)

then you might proceed with 
> end <- cumsum(rle(b)$lengths)
> start <- rev(length(b) + 1  - cumsum(rev(rle(b)$lengths)))
> # or:   start <- c(1, end[-length(end)] + 1)
> cbind(start,end)[rle(b)$values,]
     start end
[1,]     1   1
[2,]     3   4
[3,]     9  10


-- 
   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
 (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)             FAX: (+45) 35327907

use 'rle';
> a <- rnorm(20)
> b <- a < .5
> b
 [1] FALSE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE FALSE FALSE  TRUE
TRUE
[13] FALSE FALSE  TRUE  TRUE  TRUE FALSE  TRUE FALSE
> rle(b)
Run Length Encoding
  lengths: int [1:9] 1 7 2 2 2 3 1 1 1
  values : logi [1:9] FALSE  TRUE FALSE  TRUE FALSE  TRUE FALSE  TRUE
FALSE
>
__________________________________________________________
James Holtman        "What is the problem you are trying to solve?"
Executive Technical Consultant  --  Office of Technology, Convergys
james.holtman at convergys.com
+1 (513) 723-2929



                      Sean Davis
                      <sdavis2 at mail.nih.gov        To:       r-help
<r-help at stat.math.ethz.ch>
                      >                            cc:
                      Sent by:                     Subject:  [R] Finding
"runs" of TRUE in binary vector
                      r-help-bounces at stat.m
                      ath.ethz.ch


                      01/27/2005 17:13






I have a binary vector and I want to find all "regions" of that vector
that are runs of TRUE (or FALSE).

 > a <- rnorm(10)
 > b <- a<0.5
 > b
  [1]  TRUE  TRUE  TRUE FALSE  TRUE FALSE  TRUE  TRUE  TRUE  TRUE

My function would return something like a list:
region[[1]] 1,3
region[[2]] 5,5
region[[3]] 7,10

Any ideas besides looping and setting start and ends directly?

Thanks,
Sean

______________________________________________
R-help at stat.math.ethz.ch mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide!
http://www.R-project.org/posting-guide.html

Sean Davis wrote:
> I have a binary vector and I want to find all "regions" of that
vector
> that are runs of TRUE (or FALSE).
>
> > a <- rnorm(10)
> > b <- a<0.5
> > b
>  [1]  TRUE  TRUE  TRUE FALSE  TRUE FALSE  TRUE  TRUE  TRUE  TRUE
>
> My function would return something like a list:
> region[[1]] 1,3
> region[[2]] 5,5
> region[[3]] 7,10
>
> Any ideas besides looping and setting start and ends directly?
>
?rle

> Thanks,
> Sean
>
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide! 
> http://www.R-project.org/posting-guide.html
>
>
>

-- 

Kjetil Halvorsen.

Peace is the most effective weapon of mass construction.
               --  Mahdi Elmandjra




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